Until about 1970, sequential blasts were carried out almost exclusively using electric detonators that were connected to each other following the usual techniques for electrical circuits, that is, series connections and parallel connections.
These blasts were also carried out by initiating them using a detonator cord and sequencing them by means of so-called “detonator cord relays” that consisted of metal or plastic sections that would allow the donor and receiver detonating cords to be linked, inserting a specific delay time between their respective detonations.
It seems that for non-electric detonators initiated via shock tube, it was necessary to develop connection systems that allowed sequential blasts to be designed and carried out for a large number of blast-holes, which was mainly achieved by starting the blast-hole detonators via trunk lines of detonating cord or by means of surface detonators (the same for non-electric detonators initiated via shock tube).
In both cases (trunk lines of detonating cord and the use of surface detonators) duct tape was used to fix the tubes that were going to be initiated (receivers) to the detonating cord or to the detonator that was going to initiate them (donor), a slow and imprecise method that gave rise to the use of fast connectors, which were generally made of plastic.
The connectors used to initiate receiver shock tubes by means of detonators consisted of small plastic boxes inside which the detonator was housed, and they had a cover on the side which allowed the detonator tubes that were going to be initiated (receivers) to be attached and fixed to the housing of the detonator that was going to initiate them (donor), so that the axis of the donor detonator and the axes of the receiver tubes remained visibly parallel.
The drawbacks of these connectors resulted from the direction of the initiating energy of a detonator and from its excessive power, causing a large amount of shrapnel that destroyed the receiver tubes, as well as making an excessive amount of noise.
For these reasons, the next generation of connectors, the current state of the art, consists of donor detonators with a lower charge and plastic parts that allow the receiver tubes to be quickly attached to the explosive charge of the donor detonator, so that the axis of this and the axes of the receiver tubes are at right angles, with the aim of avoiding the problems of the direction of the initiating energy of the detonator's charge.
Thus, for example, U.S. Pat. No. 5,423,263 granted to Dyno Nobel Inc. on 13 Jun. 1995 discloses a connector block that transfers the initiation from a detonator inserted into the connector block to one or more shock tubes.
U.S. Pat. Nos. 5,171,935 and 5,398,611 from 15 Dec. 1992 and 21 Mar. 1995 respectively, granted to Ensign Bickford Company, describe plastic blocks with a space inside to house a low-energy detonator, the active end of which is next to a slot into which the shock tubes to be initiated are inserted.
However, reducing the charge of the donor detonator whilst keeping the same size diameter means that said charge must be concentrated into a space at the end of it, which in turn causes new problems that have been covered by different inventions, some of which aim to position the detonator more precisely within its housing.
Thus, in U.S. Pat. No. 5,499,581 granted to Ensign Bickford Company on 19 Mar. 1996, a method is described for better positioning and fixing of the initiating detonator in the corresponding casing inside the connector, by means of a moveable fixture.
On many occasions the proposed innovations aim to facilitate or improve the positioning of the receiver shock tubes in the slot next to the end of the donor detonator that contains the explosive charge.
Thus, U.S. Pat. No. 5,703,319 granted to Ensign Bickford Company on 30 Dec. 1997 describes a connector block that has houses a low energy detonator, as well as a clip forming a slot with the end of the detonator where the shock tubes to be initiated are situated.
Lastly, U.S. Pat. No. 5,792,975 granted to the same company on 11 Aug. 1998 includes several different improvements in the functionality of the connector block and provides a method for assembling the detonator inside said connector block, giving a combination of detonator and connector.
The solutions available with the current state of the art show a connector block with a housing into which a detonator is inserted that is positioned and fixed by means of various mechanisms. The explosive charge of the detonator is situated in such a way that, together with the (more or less) flexible piece that forms part of the connector block, there is a slot in which one or several shock tubes to be initiated (receivers) can be lodged.
By way of an example, international patent WO 03/023316 A1 from 20 Mar. 2003, granted to Orica Explosives Technology, discloses a device comprising a plastic connector block housing a detonator with an active end (from the initiation point of view) around which the receiver shock tubes are situated, immobilised by a clip and a closure that prevents their accidental removal.
Several problems could be linked to connector blocks manufactured according to the current state of the art, among which is the possibility of either intentionally or inadvertently separating the connector block from the detonator housed inside it and using it for purposes other than those for which it was designed and manufactured.
On the other hand, the dimensions and shapes of detonators, as well as the techniques used to manufacture the metal casing of which they are made, determine the fact that the back of the detonator is an area of irregular behaviour when there is a detonation transmission, which can cause shrapnel to destroy some of the receiver tubes or can limit the number of receiver tubes that may be initiated simultaneously.
Some solutions using energy produced on the cylindrical surfaces of the detonator, instead of the end, to initiate the tubes, require special detonators that are difficult or expensive to produce, unless one renounces the idea of using low energy detonators.
Low energy detonators have the advantage of greatly reducing the amount of metal shrapnel produced, but it does not completely avoid this.